82 
Psyche 
[March 
Most of the solitary individuals were found in grasses and forbs, but 
in frequencies proportionate to the occurrence of that type of 
microhabitat. 
There are several possible reasons why M. spinipes exhibit a habi¬ 
tat preference for the maguey plant. Agave sp. are perennial, succu¬ 
lent plants with stiff leaves capable of providing strong support for 
web attachments. These plants have lanceolate leaves with cupped 
leaf bases, radiating from a basal rosette. Such a leaf arrangement 
provides much support for the three-dimensional colonial web. 
Colinvaux (1973) suggests that plants with physiognomy similar to 
Agave sp. (i.e. Yucca ) are adapted for arid environments, in that 
their leaf shape reduces heat load, and cupped leaf bases concentrate 
moisture. Agaves might be a localized source of moisture during the 
dry season, or even at mid-day during the rainy season when solar 
radiation is intense and humidity is low. We have observed water 
accumulating at the base of some plants. There is also some evi¬ 
dence that agaves are sites of high insect activity. Debris from 
nearby flowering plants and trees and other organic matter some¬ 
times accumulates about the base of these plants. Decomposition of 
this matter and lower leaves of older agaves attracts flying insects, 
creating a microhabitat with extremely abundant prey resources. 
These findings raise questions about the nature of M. spinipes 
aggregations. Do these spiders exhibit grouping tendencies that may 
be considered social, or do they exist in fortuitous aggregations 
associated with habitat resources that are patchily distributed? 
There is some evidence that these spiders aggregate independently of 
habitat. The mean colony size of M. spinipes in two contrasted 
microhabitat sites. Agave sp. and shrubs is not significantly differ¬ 
ent (Table 1). Although other Metepeira species are associated web 
sites of a particular architecture (McCook 1889; Kaston 1948; Levi 
1977), M. spinipes is not. This species occurs in a variety of web sites 
with widely varying structure. Moreover, the shape of the web col¬ 
ony is flexible, and conforms to that of the web site. This suggests, 
at least, that coloniality of M. spinipes is independent of habitat 
structure. Spiders brought into the laboratory and released into 
cages build colonial webs, attaching silk of one animal to silk of 
another. Moreover, individuals from different colonies, even as far 
apart as several hundred miles, tolerate each other and build webs 
together (Burgess 1976). This evidence strongly suggests that M. 
